The present invention relates to a controller for an electric power assisted steering (EPAS) system for a vehicle and to an EPAS system.
In a known EPAS system comprising a controller controlling current to an electric motor which is mechanically connected to a component of the steering system, it is known to provide overall motor current limiting. For this purpose, the motor current is compared with a reference value and in the event that the motor current exceeds the reference value, power to the motor is cut off. The means which controls the power supply to the motor is supplied with a torque signal indicative of the torque applied to the vehicle steering wheel by the driver and as is well known the overall torque required to steer a vehicle generally diminishes with increasing vehicle speed. Whilst the current limiting arrangement provides a limit to the torque assistance provided by the motor and also provides protection for the motor and the drive circuits, the torque limit may not be appropriate for all driving conditions.